Method of forming a two-part coated foam structure

ABSTRACT

A foamed polyethylene product has an outer sheath of non-foamed polyethylene fused to an underlying foamed body portion. Preferably, the product is produced in an in-line method when the foam body is extruded and subsequently the skin is extruded directly on the body portion. This process only causes limited thermal degradation of an outer layer of the body portion which improves adhesion of the skin to the body portion.

This is a continuation of application Ser. No. 08/633,943 filed Apr. 17,1996 now pending.

FIELD OF THE INVENTION

The present invention relates to foamed plastic products and inparticular to foamed plastic products having an outer protective skinwhich is extruded onto a resilient foamed product. The present inventionis also directed to a method of manufacturing of the product.

BACKGROUND OF THE INVENTION

Various types of foamed plastic products are known and many of theseproducts are produced by an extrusion process and produce a body portionwhich is relatively soft and resilient. Foamed polyethylene extrudedproducts have been used for pipe insulation and have also been appliedabout structural members to provide a resilient outer cushion member.For example, foamed polyethylene cushion members have been applied tosupports of gymnastic equipment, playground equipment, footballstandards and basketball poles to reduce the possibility of injury bystriking of the structural member.

Foamed polyethylene can be extruded in a number of different shapes andis very valuable for the type of applications described above.Unfortunately, the product is relatively soft, and thus, the outersurface can tear easily, even though there is a very thin skin portionproduced at the outer surface of the product during the extrusionprocess. To overcome this problem, fabric or tape have been appliedabout the product, and thus, provides a further surface which protectsthe underlying polyethylene from damage.

It would be desirable to have a foamed polyethylene product which has atougher outer surface and one which can be produced in a cost effectivemanner.

Some solutions to the above problem have been proposed and one suchsolution involves using a separately foamed cylindrical sheath, whichwhen exposed to heat shrinks about a product. The outer sleeves areplaced about a polyethylene foamed product and then heat is applied tothe sheath which then contracts to the diameter of the foamedpolyethylene. This results in a two-stage process to marry thepolyethylene foamed body and the outer sheath and it also requiressomehow placing the foamed polyethylene body within the outer sheath.Examples of these types of structures and other arrangements aredisclosed in U.S. Pat. No. 3,607,497, U.S. Pat. No. 3,813,272, U.S. Pat.No. 3,832,260, United 10

U.S. Pat. No. 4,634,615, U.S. Pat. No. 4,776,803, U.S. Pat. No.4,780,158, U.S. Pat. No. 4,861,412, U.S. Pat. No. 4,950,352 and U.S.Pat. No. 5,360,048.

The present invention seeks to address the problems outlined above andproduce a product which can be produced at a lower cost.

SUMMARY OF THE INVENTION

A polyethylene product according to the present invention comprises afoamed body portion of polyethylene in combination with an outer skin ofnon-foamed thermal plastic polyethylene which is fused to the foamedbody portion.

According to an aspect of the invention, the foamed body portion has aboundary layer which has undergone thermal degradation and acts as anintermediary securing by heat sealing the outer skin to the bodyportion.

According to a further aspect of the invention, the skin includes asignificant amount of colour pigment and the body portion has noappreciable or consistent colour pigment.

According to a further aspect of the invention, the skin of the productincludes a significant amount of colour pigment and is of a colourunrelated to the body portion.

According to a further aspect of the invention, the outer skin includesa significant amount of ultraviolet stabilizers and the body portiondoes not have any significant amounts of ultraviolet stabilizers.

According to a further aspect of the invention, the polyethylene productwith the body portion and the outer skin is of a generally cylindricalshape with an open central cavity which is placed about an elongatemember, such that the elongate member is within the cavity whereby thepolyethylene product provides an outer resilient sheath about theelongate body member.

A method of manufacturing, according to the present invention, producesa foamed polyethylene product having an outer tough sheath about afoamed polyethylene body portion. The method comprises extruding thefoamed polyethylene body portion of a desired cross section, partiallycooling the extruded body portion, and subsequently extruding a thinthermal plastic skin directly onto the body portion, resulting in fusingor heat sealing of the skin to an upper layer of the body portion, whichdue to the heat of the extruded skin, causes limited collapse of aboundary layer of the foamed body portion and securement of the skin tothe body portion.

According to an aspect of the invention, the step of extruding the skinis conducted in-line with the step of extruding the polyethylene bodyportion and prior to complete cooling of the polyethylene body portion.

According to a further aspect of the invention, the method includes astep where the polyethylene body portion is pulled through a cylindricalextruding die which applies the extruded skin to the foamed body portionas it is pulled through the die.

According to a further aspect of the invention, the extruding dieapplies a skin having a thickness of approximately 0.003 inches.

According to a further aspect of the invention, the foamed body and theskin are of different colours.

According to yet a further aspect of the invention, 35 the cylindricaldie includes a control arrangement for adjusting the extrusion dischargerate from the cylindrical die and the method includes adjusting of thecontrol arrangement to produce a desired outer skin thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in FIG. 1, which is aschematic view of the two-stage inline extrusion process;

FIG. 2 is a cross sectional view of the foamed polyethylene body afterthe first stage of the extrusion process; and

FIG. 3 is a cross sectional view of the final product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are many known arrangement for extruding foamed polyethyleneproduct and one such extruder is shown as 2 in the Figure. Productleaves the die of the extruder at 4 and almost immediately foams to fullproduct dimensions, as generally indicated at 6. Thus, the foamedproduct 6, shortly downstream of the extruding die, is still relativelyhot, but the outer skin 7 has formed and cooling is generally occurringfrom the outside in. Often, the extruded foamed polyethylene is exposedto cooling air or water cooling to reduce the time necessary to reducethe general temperature of the polyethylene foam. This foam has lowthermal conductivity and this characteristic extends the time periodrequired to fully cool the product. In any event, shortly downstream ofthe extrusion die 4, the polyethylene foamed product passes through thecross head sheath extruder 8. This extruder is basically a cylindricalring through which the polyethylene foam is pulled and the cross headextrudes a skin onto the outer surface of the polyethylene foam usingthe foam for support.

Surprisingly, it was found that the cross head sheath extruder 8 canextrude a skin 11 directly onto the foamed polyethylene body 6 toproduce the skinned product 14. Extruding of the skin onto the bodyportion 14 only causes a limited amount of thermal degradation in thepolyethylene foam body, which thermal degradation assists in adhering orfusing the skin 11 to the body portion. It would seem that the excellentthermal insulating properties of the foamed body portion protect theunderlying layers of the foamed body portion from the highertemperatures of the hot skin and allow sufficient time for the skin tocool. There is no appreciable collapse or loss in the overall shape ofthe product. In this way, there is very little damage to the foamed bodyportion and a tough, preferably polyethylene skin can be easily appliedabout the foamed body portion.

FIG. 2 slows the foamed product 6 before extruding the skin on theproduct and FIG. 3 shows the skinned polyethylene product 14.

A further feature of the present invention is the reduction in colourpigment that may be possible, in that the outer skin can have a veryrich colour while the foamed body can be of a completely differentcolour or be essentially void of any colour pigment. Furthermore, if thefoamed core was made of recycled material, the colour of the bodyportion does not matter, as the outer sheath provides the finishedsurface.

Another advantage of the present invention is using this method to firstextrude the polyethylene foamed body and then apply a polyethylene outerskin to the foamed body. Any waste product is of polyethylene and assuch, 25 can be recycled and reused as part of the material forextruding the polyethylene foamed body. Therefore, there is no wastematerial, as any scrap product can be recycled.

The outer skin can be of a material other than polyethylene such aspolypropylene, surlyn, ethylene vinyl acetate, or other extrudablematerials which, when extruded in this manner, become sufficientlysecured to the polyethylene foam body.

The cross head sheath extruder 8 can have different cross heads fordifferent types of product, for example larger product or smallerproduct, and different cross heads for different cross sections ofproduct.

The foamed body portion 6 need not have a solid core and can have anopen center, as would be the case with pipe insulation. This shape ismost appropriate for feeding over an elongate structural member, such asa metal tube member or pipe member, and is particularly useful as acover support member for a play structure. For example, it would beuseful in protecting the support pole of a basketball hoop, forproviding protection around a roll bar, for providing protection aroundplay structures which have tubular members, such as climbing structures,and other similar types of applications.

The outer sheath also provides a very tough layer which allows otheruses for the polyethylene foamed body portion. For example, this couldbe useful for boat bumpers or protective strips where the outer skinprovides a toughness to the product which overcomes the problemsassociated with tearing of merely the body portion if it was used alone.

Another advantage of the present product is that the colour pigment canbe concentrated in the outer skin and the inner foamed body does notneed to have any particular colour pigment. This results in a costsaving and also allows a simple way to easily change the colour of theproduct during extrusion. For example, the line could be extruding oneproduct having a black coating and at an appropriate time, the rawmaterial for the cross head extruder could be replaced with a differentraw material having a different colour pigment. There would be a shortoverlap where some scrap product may have to be recycled as the crosshead extruder basically finishes extruding with the one colour andstarts extrusion with the next, but the extrusion line can basicallycontinue to run and there is no requirement to deal with changing colourregarding extruding of the foamed body portion.

A further advantage is that UV stabilizers can be placed in the outerskin and the inner foamed body does not need these stabilizers. This isimportant with respect to pipe insulation where the stabilizerssignificantly contribute to the cost of the product. By concentratingthese ISV stabilizers in the outer skin, i.e. the portion which isexposed to the sun, the body portion can be absent of these stabilizersin many cases, causing no appreciable effect on longevity of theproduct.

Although various preferred embodiments of the present invention havebeen described herein in detail, it will be appreciated by those skilledin the art, that variations may be made thereto without departing fromthe spirit of the invention or the scope of the appended claims.

I claim:
 1. A method of manufacturing an elongate composite ofindeterminate length comprising: a composite of a soft foamed hollowpolyethylene body portion of a desired cross-section and a continuousintegral outer non-foamed skin comprising the steps of continuouslyextruding the foamed hollow body along an axial length thereof;partially cooling the extruded foamed hollow body; continuouslyextruding the outer non-foamed skin through a ring orifice coaxiallyaround the foamed hollow body while ensuring a skin temperature toeffect thermal degradation and collapse of the foam of an outer boundarylayer of the foamed body to bond the skin to the body to form thecomposite without appreciable collapse or loss in the overallcross-sectional shape of the composite wherein said ring orifice iscontrolled to produce a skin thickness approximately 0.003 inches.
 2. Amethod as claimed in claim 1 wherein extrusion of said body portionproduces a foam having no significant UV stabilizers and said skincontains significant UV stabilizers forming a protective layer aboutsaid foamed body portion.
 3. A method as claimed in claim 1 wherein saidmethod includes guiding said body portion through a cross head extruderhaving a cavity to loosely receive the body allowing said body to bedrawn through said cross head extruder and engaging the productdownstream of the cross head extruder and pulling said body portionthrough the cross head extruder.
 4. A method as claimed in claim 3including cooling of the product after discharge from said cross headextruder.
 5. A method as claimed in claim 1 wherein a cross headextruder extrudes the plastic of said skin through a ring orifice ontosaid foamed body portion.
 6. A method as described in claim 1, whereinsaid step of extruding a foamed polyethylene body portion produces atubular foamed polyethylene body portion having a center cavityextending along said axial length of the body portion.
 7. A method asclaimed in claim 1 wherein said ring orifice is controllable to varysaid skin thickness.
 8. A method of manufacturing a two part structurehaving a foamed polyethylene member with an outer skin comprising:extruding a foamed polyethylene body portion of a desired cross-sectionalong an axial length thereof, partially cooling said extruded bodyportion and subsequently coaxially extruding a thermal plastic skindirectly around said body portion, to fuse said skin coaxially to theoutside of said body portion; wherein said polyethylene body portion ispulled through a cylindrical extruding die which applies said extrudedskin to said body portion as said polyethylene body portion is pulledthrough said die wherein said extruding die applies a skin having athickness of approximately 0.003 inches.
 9. A method as claimed in claim8 wherein said foamed body and said skin are of different colours.
 10. Amethod as claimed in claim 8 wherein said desired cross-section iscircular.
 11. A method as claimed in claim 10 wherein the outer skinincludes significant amounts of ultraviolet stabilizers.
 12. A method ofmanufacturing a foamed plastic member extruded along an axial lengththereof and having an outer skin comprising: extruding a foamed plasticcore of a desired cross-section along an axial length thereof; andapplying a thermal plastic skin coaxially around said foamed plasticportion to heat seal said skin to said foamed plastic core; said skinsupported by said extruded foamed plastic core wherein the skinthickness is about 0.003 inches.
 13. A method as claimed in claim 12wherein said foamed plastic core comprises foamed polyethylene.
 14. Amethod as claimed in claim 13 wherein said thermal plastic skin isselected from the group consisting of polypropylene, surlyn, andethylene vinyl acetate.
 15. A method as claimed in claim 14 wherein saidfoamed plastic core is solid.
 16. A method as claimed in claim 12wherein the heat of said skin effects thermal degradation and collapseof said outer boundary layer of said foamed body to bond said skin tosaid body.
 17. A method s claimed in claim 16 wherein said extruded skinis at a temperature to effect limited collapse of a boundary layer ofsaid foamed core to heat seal said skin to said core.
 18. A method asclaimed in claim 17 wherein said skin comprises a material selected fromthe group consisting of non-foamed thermo polyethylene, polypropylene,surlyn, and ethylene vinyl acetate.